ABSTRACT This article proposes an LLC‐type bipolar converter with a wide voltage gain range. On the primary side, two cascaded half‐bridge LLC units are used to connect to the bipolar DC microgrid. The input capacitors serve as the resonant capacitors, and a loosely coupling inductor (LCI) is adopted as the resonant inductor. Two transformers are used in the proposed converter. By modulating the phase of the two half‐bridges, the proposed converter can operate in series‐buck mode (SBuM) and parallel‐boost mode (PBoM) according to the connection relationship of the two transformers. Because the coupling phases of the LCI are different in SBuM and PBoM, the equivalent inductances of the LCI are different in the two modes, so two different voltage gain curves can be obtained to achieve a wide voltage gain in a narrow switching‐frequency range. On the secondary side, a voltage‐quadrupler rectifier (VQR) is adopted to further increase the voltage gain. Moreover, zero‐voltage switching (ZVS) can be realized for all switches in both modes. A 500‐W prototype is built to verify the effectiveness of the proposed converter.
Zhang et al. (Mon,) studied this question.